Make 'Merge' button update when MR is approved by someone else

Summary

While many things are asynchronous in the web UI, the merge button which I happen to hit many times each day - is not and requires a full page refresh after someone as accepted the MR.

Steps to reproduce

1. Create MR.
2. Have someone accept your MR.
3. Notice that the 'Merge' button does not become available after they've accepted it.

Example Project

Any.

What is the current bug behavior?

Merge button does not become available to be clicked.

What is the expected correct behavior?

After a MR is accepted, the Merge button should be available and a full page refresh should not be required.

Results of GitLab environment info

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System information
System:
Proxy:		no
Current User:	git
Using RVM:	no
Ruby Version:	2.3.3p222
Gem Version:	2.6.6
Bundler Version:1.13.7
Rake Version:	12.0.0
Redis Version:	3.2.5
Git Version:	2.13.5
Sidekiq Version:5.0.4
Go Version:	unknown
GitLab information
Version:	9.5.1-ee
Revision:	32be8c9
Directory:	/opt/gitlab/embedded/service/gitlab-rails
DB Adapter:	postgresql
DB Version:	9.6.3
URL:		https://
HTTP Clone URL:	https:///some-group/some-project.git
SSH Clone URL:	git@:some-group/some-project.git
Elasticsearch:	no
Geo:		no
Using LDAP:	yes
Using Omniauth:	no
GitLab Shell
Version:	5.8.0
Repository storage paths:

• default: /mnt/repositories/repositories Hooks: /opt/gitlab/embedded/service/gitlab-shell/hooks Git: /opt/gitlab/embedded/bin/git

Results of GitLab application Check

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Checking GitLab ... Finished

Possible fixes

(If you can, link to the line of code that might be responsible for the problem)